A wiry / weak-wooded, semi-erect to prostrate shrub, aromatic, growing to a height of 1 metre and potentially spreading to 2 metres wide.
It extends from the Northern Tablelands of NSW and the Central Coast of New South Wales. There are also records much further west in central NSW as well as in Victoria; however, these specimens appear to belong to a different taxon. A view is now held that P. denticulata (in the strict sense) is confined to the Sydney district.
It is found growing in damp areas in sclerophyll forest and woodland, usually near the coast, in sandy loamy soils, overlying sandstone.
Stems are square with rough hairs.
Prostanthera have simple, opposite and usually odorous leaves. In this species, leaves are ovate, to 10 mm long and to 3 mm wide on a petiole to 1 mm long.
Flowers have a shape described as labiate (applies to all Lamiaceae flowers) with 5 petals varying in their size, fused at their base, produced in leaf axils. One of the identification features for Prostanthera is that the 5 calyx parts (basal whorl of the flower) are fused into 2 lips.
In this species, flowers are arranged in leaf axils near the ends of branchlets with attached bracteoles to 1.5 mm long at the base. The petals are fused into a tube, to 10 mm long and wide, purple to mauve. Flowering occurs in spring and early summer
Fruits – 4 tiny nutlets (mericarps) produced at the base of the calyx.
This species is known to be cultivated and it is sold online from several outlets. It prefers a well-draining soil with morning sun and afternoon shade, so try to provide a southern to eastern aspect. It does not tolerate frost.
Needs some supplementary watering in dry times.
Can be pruned to shape – give a light tip prune after flowering to encourage a denser shrub. Could be tried in a large pot as well.
A Prostanthera in full bloom is a magnificent sight and there are so many colours to choose from for your garden. These plants are found in all states in varied soil conditions and climate and thus while it may be a challenge to grow some species many are easy in a garden situation.
A few basic growing tips are:
• Good drainage is essential. Raised beds ensure this
• Water new plants until established, weekly or as required.
• Do not over water, as this can induce root rot and fungal infestation.
• They prefer moist root runs.
• Plant drooping is an indicator of dryness
Positioning of prostantheras as border plants or near pathways is recommended as the mint odour is released when brushed against.
Plants may be grown from fresh seed. However, cuttings are frequently and reliably used, usually semi-hard wood or soft tip material, which strike well in spring or autumn.
There is a cultivar sold online called ‘Purple Haze’ which is a form of this plant.
Prostanthera is a diverse group of about 100 species, endemic to Australia, occurring in all states. There are still many unresolved taxa and species complexes, with new forms regularly being found. Natural hybrids occur between several species and most species appear to be capable of hybridizing when in cultivation. NSW currently has about 52 species, some of which are species-complex and others which are threatened with extinction.
This genus is currently under revision, and several species complexes are unresolved. Natural hybrids occur between several species and most species appear to be capable of hybridizing when in cultivation.
Some 80% of mints contain aromatic oils within their leaves with oil of cineol being a major component. Prostanthera sieberi, P. incisa and P. staurophylla are quite pleasantly overpowering due to their exudates when crushed.
Positioning of prostantheras as border plants or near pathways is recommended as the mint odour is released when brushed against. Oil from the leaves of some species is distilled for use in cosmetics and as soap additives.
Most prostanthera regenerate from seed after fire, with many species taking up to 12 months to appear.
Prostanthera – from the Greek prosthike (προσθήκη) which translates to “addendum”, and anthir (ανθήρ) meaning anther – referring to the anthers which have an appendage of tissue.
denticulata – Latin meaning “with small teeth” referring to the edges of the leaves.
This species is not considered to be at risk of exctinction in the wild.
NSW Flora Online (PlantNET) – Prostanthera denticulata profile page https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Prostanthera~denticulata
Australian Native Plants Society Australia – Prostanthera – The Mint Bushes Information Page
Wrigley, J.W. & Fagg, M.I. (2001). Australian Native Plants – Propagation, cultivation and use in landscaping. 4th edition. New Holland Publishers, Pty. Ltd. Australia.
Wikipedia – Prostanthera denticulata profile page